What does the following question mean? & what is its answer?

Question

how many instances of an abstract class can be created?

Answer 1

To instantiate a class means "create a new object described by the class":

abstract class SomeClass {};
SomeClass obj = new SomeClass();

An abstract class cannot be instantiated because it does not have a complete implementation.
It is just useful, like interfaces, for inheritance.

Difference between abstract classes and interfaces:
http://net-informations.com/faq/net/abstract.html